Snow, Ice and Extreme Cold

Key Points

Most of the time Seattle's winter weather is controlled by the Pacific Ocean which remains relatively even in temperature throughout the year. Occasionally, however, cold air from the interior of the continent pushes into the Puget Sound region and causes dramatic cold spells, ice and snow.

While Seattle does not receive as much snow on average as other parts of the country, snowfall is not uncommon and can be very heavy.

Accurate weather records began only about 100 years ago, but based on historical accounts, Seattle's winters seem to have been colder and snowier in the 19th and early 20th centuries.

Meteorologists have made great strides in forecasting snow and ice storms. Roughly 80 percent of snow storms in the Puget Sound lowlands occur when cold air from the interior of the continent pushes through the Frasier Gap near Bellingham and meets a low pressure system coming off the ocean. If the cold front lingers, snow and ice can be on the ground for weeks[i].

The main effect of snow is the impairment of transportation. Because nearly all social and economic activity is dependent on transportation, snow can have a serious impact. Most of the effects are cumulative, so the longer transportation is impaired, the greater the impacts.

Some of the most significant impacts from snow are:

Seattle does not have dedicated snow plows, trucks have to be outfitted with snow removal equipment when snow threatens.

Public safety impacts resulting from the inability to get emergency vehicles where they need to go.

Utility outages as power demand peaks and pipes freeze. Power losses during extreme cold have resulted in deaths from carbon monoxide poisoning as some people attempt to keep warm by lighting charcoal fires indoors.

Economic losses due to business closures and lost wages by workers unable to get to work or required to stay home with children when schools and childcare close.

Even with all trucks have been outfitted with snow removal equipment, there is not enough of them to plow every street in the city.

Due to Seattle's steep topography, some streets are too steep to keep open during snow and ice events.

The Seattle Department of Transportation and King County Metro developed new snow and ice plans following the challenges of the 2008 snow and ice storm. The new plans stress increased use of salt, more pre-staging of snowplows, better gathering of information about conditions of streets and buses and better communication with the public.

During snow and extreme cold, Public Health - Seattle & King County issues public warnings about the dangers of carbon monoxide poisoning. A regional "Take Winter by Storm" campaign also helps educate on winter preparedness and safety.

Occasionally, rapidly melting snow can contribute to saturating the ground and becomes a factor in triggering landslides. The last time this happened was in the winter of 1996 and 1997.